1. Field of the Invention
The present invention relates to a high-speed difference pulse code modulation (DPCM) coder, comprising a quantizer and a calculating unit which serves to determine the estimated value and which contains adders, subtractors and multipliers.
2. Description of the Prior Art
The difference pulse code modulation processes frequently used in digital transmission or storage of signals. In this process, an estimated value s.sub.i of a current sample s.sub.i is calculated on the basis of a preceding sample value s.sub.i-k. The difference .DELTA.s.sub.i 32 s.sub.i -s.sub.i is quantized and subsequently transmitted. The aim of the process is to use a shorter word length to represent .DELTA.s.sub.i then is required to represent the PCM signal values s.sub.i. The requisite transmission rate and storage space requirement are therefore reduced. FIG. 1 of the present application illustrates a simple DPCM loop whose function will be explained in greater detail. The estimated value s.sub.i is calculated in four steps. These four calculating steps must be executed within a length of time which corresponds to the interval of time between two consecutive PCM signal values s.sub.i, s.sub.i+1. At high data rates only a short length of time is available for these four calculating operations, which means that it is difficult or impossible to use this process even when the most modern circuit technology is employed.